Intrusion alarm system

ABSTRACT

A wireless point of entry intrusion alarm system having a central monitor and alarm cooperates with magnetically actuable entry detectors placed at potential entry locations. Each sensor is automatically reset by the same magnetic means upon reclosure of the guarded entry.

Db-.1. 1D

Fmm

Oct. 3, 1972 [56] References Cited [54] INTRUSION ALARM SYSTEM XXX 44 22 C 2 2 O0 //5 002 44 33% m mm T 6 mm A P w s wn EMn T e AMDm T S 60 we?W999 111 m 2 2 .l 111 7 7 6 0O 9 5 403 494 5 3 3 3 C .ns m x HM n m O nm m .mm a a m L m r s 0 m w c 0 1 m FmR d V. mm," a m. @MS S e m m m .ev I A l 2 3 7 7 [22] Filed: Jan. 26, 1971 Primary Examiner-David L.Trafton Attorney-Samuel C. Yeaton [21] Appl.No.: 109,866

52 US. Cl. ..................340/224, 325/105, 325/169, ABSTRACT Awireless point of entry intrusion alarm system hav- 340/274 .G08b 13/08ing a central monitor and alarm cooperates with mag- .340/224, 274',325/105, 115, netically actuable entry detectors placed at potential 3251 9 1 5 entry locations. Each sensor is automatically reset by the samemagnetic means upon reclosure of the guarded entry.

[51] [58] FieldofSearch.....

8 Claims, 3 Drawing Figures mm @[pi MULTI VI BRATOR OSClLLATOR ALARMPOWER SOURCE PATENTEU OCT 3 I972 II. I

HII F|G.lo.

. U la FlG.lb.

RECEIVER Q INVENTORS GER/1L0 F. R055 HUGH MAGU/RE ATTORNEY MULTI VIBRATOR ALARM POWER SOURCE 41% OSCILLATOR FIG.2.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionpertains to means for providing protection of buildings or otherelements of property from forced entry or unauthorized treatment andmore specifically relates to magnetically actuable radio signaltransmission devices for detecting the unauthorized entry of buildingsor for detecting unauthorized access to or movement of guarded property.

2. Description of the Prior Art Prior art intrusion devices of manytypes have served advantageously in the protection of lives and propertyfrom intruders, but. generally have been complex, expensive, anddifficult to install and maintain. There has been an unfulfilled needfor inexpensive and easily installed and easily operated intrusionsensing apparatus which has the reliability of such prior devices, butwhich offers greater economy of ownership and flexibility of use. Manyprior devices require relatively large batteries and charginginstallations for their successful operation. Others use permanentwiring which is complex to install even in a building while underconstruction. Sensing systems that depend on the physical breaking ofelectrical contacts have not afforded great reliability, as well asbeing difficult to install and to conceal. For example, the kind ofalarm sensor using conductive tapes fastened to the glass of windows isexpensive and difficult to install and maintain. Further, it isparticularly sensitive to development of high false alarm rates as thecondition of the building degrades and causes misalignment of electricalcontacts. False alarm rates are high where sensors are used that noticedisturbances in sonic or electromagnetic standing wave fields.

SUMMARY OF THE INVENTION The present invention relates to a wirelessalarm system for providing protection of buildings or of other propertyfrom unauthorized entry or removal. The intrusion system utilizes acentrally located radio receiver and alarm system cooperating withmagnetically actuable radio transmitters placed at points of possibleentry. Each transmitter is furnished with a magnetically actuatedcondenser charging circuit having a very low cur rent drain demand on anassociated miniature battery. Further, each transmitter is magneticallyactuated upon the event of an intrusion to transmit a short, low energylevel signal to the centrally located receiver for actuating an alarm.No further transmission is made by the affected transmitter until it ismagnetically reset, for instance, by the manual closing of theassociated entry.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are respectiveelevation views of two situations showing a representative installationof the novel intrusion sensor.

FIG. 2 is a circuit diagram illustrating the electrical connection ofcomponents of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1A illustrates one mannerof use of the novel intrusion sensor 1 with its associated antenna 3when affixed to a stationary part or frame 5 of a window 4, that window4 to be monitored against unauthorized entry. Closely associated withintrusion sensor of detector 1, when the movable part of window orbarrier 4 is in its normal closed position, is a small bar magnet orother source of magnetic field 2 affixed to window 4 by an adhesive orother conventional fastening means. The intrusion sensor 1 and magnet 2may be installed permanently or temporarily by untrained personnel andmay readily be shifted from one location to another since no electricalwiring is required. In such a manner, sensors may be installed to detectthe opening of a window, door, sky light, or roof hatch or to detect anunauthorized act causing relative movement between a magnet placed on anexpensive object of art relative to a sensor affixed to the wall fromwhich the object is supported.

Opening of an entry such as the window 4 of FIG. 1A is illustrated inFIG. 1B. It is seen that by raising the frame of window 4, magnet 2 isremoved from the proximity of sensor 1, and sensor 1 is no longeraffected by the magnetic field of magnet 2. Sensor 1 is thereby causedto transmit a short duration alarm signal via antenna 3 to a centralreceiver 51 yet to be described in connection with FIG. 2.

The general disposition of sensor 1 and magnet 2 in FIGS. 1A and 1B isintended to be illustrative of one of many ways of using the apparatus.If desired, elements 1, 2, and 3 may be mounted in a completelyconcealed manner. Various other alternative configurations will beapparent to those skilled in the art, all permitting sensor 1 to sense acharacteristic of an element in a normal position (open or closed) andto sense a change of the element from its normal position induced by theremoval of the normal magnetic field from proximity to sensor 1.

Referring now to FIG. 2, details of the intrusion sensor 1 of FIGS. 1Aand 1B will be described; it will be understood that the intrusionsensor 1 is normally placed adjacent an avenue of possible entry so thatits element 10 sensitive to the position of magnet 2 is close to magnet2 when the window, door, or other entry barrier is in a normal position,such as a closed position. Sensitive element 10 is a conventional singlepole, double throw, dry reed switch, though other reed switches or otherswitches capable of changing state according to the presence or absenceof a magnetic field of predetermined level may alternatively beemployed. In a preferred embodiment, reed switch 10 has contactbearingleads 1] and 12 supported in generally parallel relation at one end 13of a hermetic envelope 14. At the opposite end 15 of switch 10 is a lead16 similarly sealed within envelope 14 and supporting a contactbearingswitch blade spring 17. Lead 16 is coupled through low internal leakagecondenser 20 to ground.

Lead 1 l is connected through charging resistor 21 to the positiveterminal of battery or other electrical source 22. The second terminalof battery 22 is grounded. On the other hand, lead 12 of switch 10 iscoupled through resistor 23 to ground and also to the gate electrode offield effect transistor 24. The source electrode of transistor 24 isgrounded, while its drain electrode is connected through solenoid 31, inwhich a second switch 30 is immersed, to the positive terminal ofbattery 22.

Switch 30 may be generally similar to switch in that it may be aconventional dry reed switch, but having a single pole, single throwcharacteristic whose conductivity state is determined by the presence orabsence of a magnetic field generated by the surrounding solenoid orcoil 31. For example, switch 30 may comprise a hermetic envelope 32 withleads 33 and 34 projecting through its ends to support the respectiveinternal contact-bearing switch blade springs 35 and 36. Switch 30 isconnected at its lead 33 to a positive pole of battery 22 and at lead 34to a transmitter device yet to be explained that comprises, in seriesrelation, multivibrator 40, oscillator 41, and antenna 3.

In one form of the apparatus, the sensor 1 employed a 9 volt battery 22,the charging resistor 21 was 1 megohm, resistor 23 was 82,000 ohms, andcondenser 20 was 10 microfarads; subminiature elements are usedthroughout.

The output of switch 30 on lead 34 is the input to a conventionalmultivibrator circuit 40. Multivibrator 40 is a free running circuit,when supplied with the input signal, whose output serves as a modulationsignal, as will be seen. Multivibrator 40 is preferably of the simpleconventional type producing a semi-square low audio frequency waveoutput with a comparatively slow rise time, the wave having a frequency,for example, of 1 KHz. On the other hand, either amplitude, frequency orpulsed modulation may be employed.

Multivibrator 40 serves as a modulator for oscillator 41, in effectturning it on and off. Oscillator 41 may be an inexpensivecrystal-controlled oscillator operating, for example, at a 100 milliwattlevel at a suitable carrier radio frequency, such as 27.255 MHZ.Modulator 40 produces 100 per cent modulation of the carrier radiofrequency within oscillator 41, and its limited rise time characteristicsatisfactorily limits the harmonic content of the output radio frequencysignal. The output of oscillator 41 is radiated into space by antenna 3,which may comprise a simple conventional un-tuned wire antenna. Theduration of the output or pulse burst is minimized for the purpose ofpreserving the life of battery 22. However, it is also desired toprevent false alarms, such as may be triggered by electrical storms.Thus, an optimum duration when using amplitude modulation may be on theorder of 1 second.

FIG. 2 illustrates the situation arbitrarily defined as normal forpurposes of explanation, when window 4 is closed, so that magnet 2 is atits closest proximity to sensor 1; Le, window 4 is in the position shownin FIG. 1A. In this condition, switch blade spring 17, being constitutedof magnetic material, is held by the magnetic field of magnet 2 againstthe contact-bearing lead 11 of switch 10, as illustrated in FIG. 2. Inthis same normal situation, switch 30 is non-conducting, their springcharacteristics holding switch blade springs 35 and 36 apart. In thisstate, condenser 20 has normally been charged from battery 22 through apath including charging resistor 21, lead 11, switch blade spring 17,lead 16, and ground. Charging of condenser 20 is slow, since the timeconstant of the R-C circuit comprising resistor 21 and condenser 20 isquite large. Thus, the

maximum current drain to which battery 22 is subjected is very low, andbattery 22 has a life substantially equal to its normal shelf life.

Should magnet 2 be moved so that its magnetic field no longer influencesreed switch 10, the spring nature of switch blade spring 17 forces it tobreak the circuit between resistor 21 and condenser 20. Instead, acircuit between condenser 20 and lead 12 is established; thus, a voltageis developed across resistor 23. Such an event causes field efiecttransistor 24 to conduct and current from battery 22 is allowed to flowthrough coil 31 and transistor 24 to ground. The magnetic fieldgenerated by coil 31 consequently causes switch blade springs 35 and 36of reed switch 30 to come into contact with one another. The modulatingmultivibrator 40 is then caused to supply its semi-square wave outputwave to high frequency oscillator 41. Pulsed radio frequency carrierenergy is thereby transmitted by antenna 3.

Transmission from antenna 3 continues for a short time, for example,about one second and is ended when the charge stored on condenser 20 isdissipated. Thus, the voltage across resistor 23 fails to maintain fieldeffect transistor 24 in its conducting state, reed switch 30 is opened,and the supply of an excitation signal to multivibrator 40 ends, endingoperation of oscillator 41. Thus, if window 4 remains open, no furtherdrain is imposed on battery 22. However, sensor 1 is automatically incondition to be recycled by shutting window 4 and thus reestablishing acharging circuit for condenser 20 from battery 22 through chargingresistor 21 and reed switch 10. The sensor thereafter operates each timeits associated window or other entry barrier is opened, radiating oneshort train of radio frequency energy pulses once for each such openingevent, and being reset for the next opening event by each successiveclosure of the entry barrier.

It will be understood that a plurality of sensors 1 may be used in adwelling or business building or other location, one at each door,window, or other potential entry. Each may be provided with anidentifying radiation characteristic merely by adjustment of therelative modulating frequency of the corresponding free runningmultivibrator. In a simple form of the system, all modulationfrequencies may be substantially the same. The radiated carrier train,when received by an antenna 50 of a central monitor receiver 51, may bedemodulated therein for the purpose of supplying the audio signal to analternating current sensitive relay within receiver 51. Operation of therelay may supply power to a device 52 for producing a sustained visualor audible alarm within the building or outside of it. Receiver 51 andalarm 52 may be supplied from a common power source if desired.Operation of receiver 51 may alternatively or additionally supply analarm signal via telephone lines to a conventional alarm device at acentral police station or detective agency. Where discrete modulationfrequencies characterize the several sensors used in a building, theseveral differentfrequency signals provided by sensors with adjustablefrequency multivibrators may be demodulated by receiver 51 and suppliedthrough corresponding audio frequency filters to activate relays whichlight tell-tale lamps (not shown). Such relays would preferably latch inthe activated position so that a display indicating the location of thedisturbed entry is readily afforded. Unauthorized movement of a safe, adisplay case, valuable painting, or the like may be similarly signalledlocally or at a police headquarters. Where the system supplies alarmsignals to a remote headquarters, the owner has the option of disablingreceiver 51 when present in the protected building by operating switch54 and observing the state of indicator lamp 55. He may similarlydisable the connection to alarm 52 in his presence so that policeheadquarters will not be subjected to false alarms when the buildingentries are permissibly used. Receiver 51 may be adapted to handleinputs from other conventional sensor devices, such as smoke or firedetectors. i

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than of limitation and that changes within thepurview of the appended claims may be made without departure from thetrue scope and spirit of the invention in its broader aspects.

We claim: 1. An intrusion alarm system for detecting relative motionbetween first and second parts comprising:

magnetic field generating means affixed to one of said parts, firstswitch means having first and second states with respect to first andsecond magnitudes of said magnetic field, respectively, charging circuitmeans operative in series circuit relation only when said first switchmeans is in said first state, comprising: electrical current sourcemeans, first resistor means, and capacitor storage means, alarm actuatorcircuit means operative in series circuit relation only when said firstswitch means is in said second state comprising: said capacitor storagemeans, voltage sensing means for providing an output signal when thevoltage stored on said capacitor storage means exceeds a predeterminedvalue, and said electrical current source means, second switch meansresponsive to said output signal by changing from a non-conducting to aconducting state, and alarm circuit means operative in series relationwith said second switch means only when in said conducting statecomprising:

said electrical current source means,

multivibrator means, and

oscillator means for transmitting an alarm signal. 5 2. Apparatus asdescribed in claim 1 wherein said oscillator means is responsive to saidmultivibrator means for producing a train of pulsed radio frequencysignals for space transmission.

3. Apparatus as described in claim 2 wherein said multivibrato means isadapted to produce an audio frequency semi-square wave output with risetimes suf ficiently slow for substantially limiting the harmonic contentof the output of said radio frequency oscillator means.

4. Apparatus as described in claim 1 wherein said first switch meanscompris gs single pole, double throw reed switch means having irst,second, and third electrical terminal means,

said first terminal means supports said double throw reed, and

said reed supports contact means for contacting said first or secondterminal means with respect to the magnitude of said magnetic field.

5. Apparatus as described in claim 4 wherein:

said first terminal means is connected to said capacitor storage means,

said second terminal means is connected to said first resistor means,and

said third terminal means is connected to said second resistor means.

6. Apparatus as described in claim 4 wherein said second switch meanscomprises:

magnetically actuatable single pole, single throw reed switch meansconnected to said electrical source means, and

solenoid magnetic field generating means connected to said electricalsource means for actuating said magnetically actuatable single pole,single throw reed switch means.

7. Apparatus as described in claim 6 wherein said voltage sensing meanscomprises transistor switch means for controlling current flow throughsaid solenoid magnetic field generating means when said voltage dropacross said second resistor exceeds a predetermined value.

8. Apparatus as described in claim 1 including remotely located receivermeans indicating reception of said pulsed radio frequency spacetransmitted signals for alarm purposes.

1. An intrusion alarm system for detecting relative motion between firstand second parts comprising: magnetic field generating means affixed toone of said parts, first switch means having first and second stateswith respect to first and second magnitudes of said magnetic field,respectively, charging circuit means operative in series circuitrelation only when said first switch means is in said first statecomprising: electrical current source means, first resistor means, andcapacitor storage means, alarm actuator circuit means operative inseries circuit relation only when said first switch means is in saidsecond state comprising: said capacitor storage means, voltage sensingmeans for providing an output signal when the voltage stored on saidcapacitor storage means exceeds a predetermined value, and saidelectrical current source means, second switch means responsive to saIdoutput signal by changing from a non-conducting to a conducting state,and alarm circuit means operative in series relation with said secondswitch means only when in said conducting state comprising: saidelectrical current source means, multivibrator means, and oscillatormeans for transmitting an alarm signal.
 2. Apparatus as described inclaim 1 wherein said oscillator means is responsive to saidmultivibrator means for producing a train of pulsed radio frequencysignals for space transmission.
 3. Apparatus as described in claim 2wherein said multivibrato means is adapted to produce an audio frequencysemi-square wave output with rise times sufficiently slow forsubstantially limiting the harmonic content of the output of said radiofrequency oscillator means.
 4. Apparatus as described in claim 1 whereinsaid first switch means comprises single pole, double throw reed switchmeans having first, second, and third electrical terminal means, saidfirst terminal means supports said double throw reed, and said reedsupports contact means for contacting said first or second terminalmeans with respect to the magnitude of said magnetic field.
 5. Apparatusas described in claim 4 wherein: said first terminal means is connectedto said capacitor storage means, said second terminal means is connectedto said first resistor means, and said third terminal means is connectedto said second resistor means.
 6. Apparatus as described in claim 4wherein said second switch means comprises: magnetically actuatablesingle pole, single throw reed switch means connected to said electricalsource means, and solenoid magnetic field generating means connected tosaid electrical source means for actuating said magnetically actuatablesingle pole, single throw reed switch means.
 7. Apparatus as describedin claim 6 wherein said voltage sensing means comprises transistorswitch means for controlling current flow through said solenoid magneticfield generating means when said voltage drop across said secondresistor exceeds a predetermined value.
 8. Apparatus as described inclaim 1 including remotely located receiver means indicating receptionof said pulsed radio frequency space transmitted signals for alarmpurposes.